1. Field
The present disclosure relates to a fuel cell stack.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell includes a membrane electrode assembly (MEA), in which an anode electrode is disposed on one side of a solid-polymer electrolyte membrane and a cathode electrode is disposed on the other side of the solid-polymer electrolyte membrane. The solid-polymer electrolyte membrane is made from a polymer ion-exchange membrane. The MEA and a pair of separators, sandwiching the MEA therebetween, constitute a power generation cell. A predetermined number of such power generation cells are usually stacked and used, for example, as a vehicle fuel cell stack for a fuel cell vehicle (such as a fuel cell electric automobile).
In a fuel cell stack, the temperatures of some power generation cells tend to decrease more easily than other power generation cells due to dissipation of heat to the outside. For example, heat of a power generation cell disposed at an end of the fuel cell stack in the stacking direction (hereinafter, referred to as an “end cell”) is easily dissipated through a terminal plate, an end plate, and the like, which are disposed adjacent to the end cell. Therefore, the temperature of the end cell significantly decreases. As a result, a problem arises in that retention of water may occur in the end cell and power generation performance may decrease.
An example of a fuel cell stack for solving the problem is disclosed in Japanese Unexamined Patent Application Publication No. 9-92322. The fuel cell stack includes a pair of fuel cell substacks, in each of which a plurality of fuel cell cells are stacked, and a gas-impermeable unit disposed between the pair of fuel cell substacks. The gas-impermeable unit blocks flows of a fuel gas and an oxidant gas between the fuel cell substacks.
The fuel gas and the oxidant gas each flow independently in each of the fuel cell substacks, and the flow rate of the oxidant gas has such a distribution that the flow rate is high in both end portions of the fuel cell stack and low in a central portion of the fuel cell stack. It is described that such a distribution of the flow rate of the oxidant gas cancels out the temperature distribution of the fuel cell stack, in which the temperatures of the both ends portions are high and the temperature of the central portion is low; and thereby the amounts of water held in electrolyte membranes of the fuel cells are made uniform.